1. Field of the Invention
This invention relates generally to a method and apparatus for monitoring transformers, and more particularly, to a continuous on-line transformer monitoring and analysis method and apparatus using a plurality of monitors to determine transformer performance.
2. Description of the Prior Art
The availability of power transformers is a key factor in the overall availability of a power transmission system. The reliability of the transformer, including the insulation and cooling systems, and the maintenance required during its useful life have a significant impact on availability. Decisions about the operating condition of the transformer and its attendant systems are typically based on a single parameter monitored over a relatively short time. At times, the result of such a test is unscheduled transformer downtime for maintenance, inspection, or repair. By increasing the knowledge of long-term changes in the operating condition of a power transformer, more accurate decisions can be made and the required action scheduled to reduce or eliminate unscheduled downtime. Since most problems with power transformers occur slowly over a long time, continuous monitoring of certain parameters and access to real-time data of the operational parameters of a power transformer is needed to analyze changes in the transformer's condition or health.
The need for continuous monitoring of power transformers has developed from the increased use of dissolved gas-in-oil and oil analysis, both manually sampled with the analysis performed in a laboratory every six to twelve months. Such a periodic analysis does not provide real-time or current data regarding transformer condition. Also, an historical analysis of data for each transformer can provide the following benefits to the operating utility: major reductions in unscheduled transformer downtime, major reductions in frequency of catastrophic failures, reduced repair costs, reduced maintenance, and the establishment of an historical data base for each transformer. Whereas present cooling control systems make decisions based on a single monitored parameter, such a transformer monitoring system could operate the transformer cooling system based on the results from several monitored parameters. Better decisions based on more data would provide improved transformer availability.
Thus, it would be desirable to develop a continuous on-line system for monitoring and analyzing the operating conditions of a transformer. Such a system could determine changes in the operating condition of a transformer based on an historic data base and identify potential problems before they become major or catastrophic. The problem can then be addressed during scheduled maintenance, or immediately, if necessary. Such a system could also provide improved reliability and predictability for operation of the transformer cooling system.
The present invention provides these desired benefits in the form of a microprocessor-based transformer monitoring system. Using a number of sensors and signal conditioners located within or near the transformer, the transformer monitoring system provides real-time on-line data collection and analysis for determining the transformer's condition, operating the cooling system, and determining whether more extensive analysis or a load reduction is advisable. The transformer monitoring system maximizes transformer availability through early detection of problems requiring immediate correction and proper analysis of less-serious problems not requiring immediate action. More reliable analysis and alarm activation are provided by monitoring several parameters, rather than the single parameter of prior art techniques. The present system can also be expanded with additional sensors and signal conditioners as they become available.